Process of working copper alloys aud more particularly copper alloys containing less than about 12% tin



Patented May 4, 1937 UNITED STATES PATENT OFFICE PROCESS OF WORKING COPPER ALLOYS AND MORE PARTICULARLY COPPER AL- LOYS CONTAINING 12% TIN Rudolf Otto Barthel,

Germany, assignor to ration, New York, N. York.

No Drawing. Applicatio No. 739,266. In Germany August 17, 1933 LESS THAN ABOUT Frankfort-on-the-Main, American Lurgi Corpo- Y., a corporation of New n August 10, 1934, Serial 6 Claims. (Cl. 148 -115) "showed marked coring or segregation of tin towards the edges of the dendrites. Due to the coring effect which occurred during solidification,

copper alloys containing over about 6% tin, as cast, consisted not only of alpha solid solution, but also-of a second constituent which was the brittle delta compound which separated between the cored alpha dendrites. -As a result of the brittleness of the delta constituent,its presence greatly reduced the plasticity andductility of the i copper alloy, and rendered it diflicult to work, es-, pecially in the cold state.

Attempts have been made to obtain a homogeneous copper alloy. Thus, in the homogenizing of copper-tin alloys, the treatments were lengthy and expensive. For instance, it was proposed to homogenize copper-tin alloys by a heat treatment at a high temperature for a prolonged period of time. Moreover, in actual practice, the cast metals were subjected to a long series of cold working operations with expensive and troublesome intermediate annealings. Under these prior conditions, the presence of the delta constituent caused the metal to harden very rapidly while undergoing cold work. Consequently, a large amount of reduction in the cold state was not possible without frequent intermediate annealing operations Thus, the workability and other physical properties of phosphor-bronze contain ing over 6% tin and upto about 12% tin were attempted to be improved by repeated cold drawing of cast ingots, billets, etc. and by intense annealing between drawings at suitable temperatures. In order to manufacture rods, wire and tubes, according to prior processes, it was necessary to use up to about 12 or more annealings-and up to about 15 cold working operations depending upon the final dimensions desired. To facilitate the cold working, prior investigators endeavored to have the material in a homogeneous state because of the increase of ductility and of related properties. Difficulties were encountered in attempting to obtain homogeneous structures and in case of products having large cross-sections, it was practically impossible to obtain complete homogenization. When simple or single drawing operations were employed, it was not possible to obtain a thorough working or kneading throughout the cross sectional area and inand to the core of the product. 'In other words, rigidity or.

a lack of plasticity still prevailed in the core of the product.

It is an object of the present invention to overcome the aforesaid disadvantages of the prior processes and to provide a process which is wholly satisfactory in practical commercial operations on an industrial scale.

It is another objectof the invention to provide a process of treating copper alloys, containing about 6 to about 12% tin to convert the same to a homogeneous condition and to an alpha state.

, A further object of the invention is the provision of a relatively simple procedure which can be used to produce a variety of products including rods, tubes, wire, and the like.

Other objects and advantages will become apparent from the following description of the invention.

Generally speaking, the present invention contemplates the elimination of prior shortcomings by subjecting the cast ingot, billet, etc. to a homogenization process at an elevated temperature. This homogenization is brought about by plas tically kneading, forming or working such ingots, billets, etc. at special elevated temperatures before cold drawing or working. In applying the present process, shaping or forming of the ingot, billet, etc. may be effected which eliminates a number of hot and cold drawing operations and intermediate annealings. Plastic kneading, forming or working together with forming or shaping may be brought about by extruding the ingots, billets, etc. of a copper alloy containing about 6 to about 12% of tin in an extrusion press. Certain special conditions must be observed which are not obvious from the customary'extrusion processes. Thus, the temperature at which the aforesaid copper alloy is subjected to kneading, extruding, or working, is controlled within critical limits closely coordinated to the composition of the alloy.

It was found that unexpected results could be obtained if the cast metal was hot worked according to the present invention at critical temperatures between about 500 to 650 C. As a result of experiment, it was discovered that the lower the content of tin the higher the temperature. Thus, for instance, a copper alloy with approximately 8% of tin and about 0.3%

620 C. With a copper alloy containing about 6% tin, it was discovered that a temperature,

of about 650 C. was required. For the copper alloys within the contemplation of the present invention, it was discovered that a special temperature range of about 500 C. to about 650 C. was essential. It was found that by proceeding in accordance with the principles of the present invention and by subjecting the cast copper alloys to intensive and thorough kneading, etc., at the aforesaid special temperatures, diffusion of the tin may be surprisingly accelerated and homogenization may be completed within a remarkable short time to produce new results.

When manufacturing articles of large crosssection, where the alloy does not undergo much reduction from theoriginal casting to the finished product, it is advantageous to first subject the ingot billet, etc. to a cold pressing operation, preferably to an extent of about 10 to about 20%, and then to hot work, knead, extrude, etc. the same. For instance, an ingot of the aforesaid copper-tin alloy may be cast with a diameter smaller than that of the receptacle of the extrusion press and then introduced into. said receptacle in a cold state and compressed to the diameter of the receptacle. After this opera- 7 tion, the ingot may be heated to a special temperature as described hereinabove and then subjected to a hot extrusion-or a thorough kneading operation. Even in the case of a relatively small reduction of cross-section, the copper alloy was found to have been brought to a practically complete homogeneous state.

The present process can be applied to coppertin alloys containing about 6-12% tin. The

alloys may contain deoxidizing agents such as phosphorus, lithium, sodium, silicon, magnesium, beryllium, etc., or other alloying elements, such as nickel, which are capable of producing any desirable physical or other properties.

It is to be observed that the present process is of special advantage for manufacturing rods and tubes from which bearings are made. In this manner, it is possible to extrude in one step a tube having a cross-section of about 50 to mm. from a cast copper alloy containing about 8 to 9% tinand 0.1 to 0.3% phosphorus. After extrusion, the alloy was found to be so homogeneous that the subsequent process of cold drawing only had to be applied to give the tube the desired form or shape.

It is also to be noted that by the present process copper alloys, such as bronzes containing about 6 to 12% tin, may be homogenized and brought to the alpha condition at lower temperatures and in a much shorter time than it has been possible heretofore.

Furthermore, the copper alloys described herein and homogenized according to the present invention have deep drawing properties and can be drawn into rods, tubes, wires, etc. without intermediate annealing.

Although the present invention has been described with respect to preferred embodiments, it is to be observed that variations and modifications may be resorted to by those skilled in the art without departing from the scope and spirit of the present invention as defined by the appended claims.

I claim:

1. The process of treating copper-tin alloys which comprises cold working a cast copper alloy containing about 6 to about 12% of tin to an extent of changing at least one of its dimensions by about 10 to about 20% and subjecting the cold worked alloy to plastic forming at elevated temperatures of about 500 C. to about 650 C. whereby the structure of the alloy is converted practically entirely to an alpha state.

2. In the process of treating copper-tin alloys, the improvement which comprises casting a copper alloy containing about 6% to about 12% of tin, rapidly cooling said alloy whereby an alpha plus delta structure is produced, hot working said alloy at a temperature of about 500 C. to about 650 C., to convert said alpha plus delta structure practically completely to an alpha state, and subjecting said alloy substantially devoid of delta phase to cold working.

3. In the process of treating copper-tin alloys,

. the improvement which comprises casting a copper alloy containing about 6% to about 12% of tin and about 0.1% to about 0.3% phosphorous, rapidly cooling said alloy whereby an alpha plus delta structure is formed, and extruding said alloy at a temperature of about 500 C., to about 650 C., to convert said alpha plus delta phase practically completely to an alpha state.

4. In the process of producing homogeneous copper-tin alloys practically devoid of delta phase, the improvement which comprises casting a copper alloy containing about 6% to about'12% of tin, rapidly cooling said alloy whereby an alpha plus delta phase is formed, and subjecting said alloy to hot kneading at a temperature of about 500 C., to about 650 C., whereby said alpha plus delta phase is converted practically completely to an alpha state.

5. In the process of producing homogeneous copper-tin alloys substantially devoid of delta structure, the improvement which comprises rapidly cooling a copper alloy containing about 6% to about 12% tin whereby an alpha plus delta structure is produced, subjecting saidalloy to a single hot extrusion at elevated temperatures of about 500 C. to about 650 C. whereby said alpha plus delta structure is practically completely converted to an alpha state.

6. In the process of producing homogeneous copper-tin alloys, the improvement which comprises rapidly cooling a copper alloy containing about 6% to about 12% tin, subjecting said alloy having an alpha plus delta structure to hot extrusion at an elevated temperature of about 500 C. to about 650 C., the aforesaid elevated temperature varying inversely with the tin content and the lower the tin content the higher the temperature whereby said alpha plus delta structure is converted practically completely to an alpha state.

RUDOLF OTTO BARTHEL.

iii

(ill 

